Electrorheological fluids and charged suspensions

EIS characterization of electrorheological fluids (ERF) represents an interesting subsegment of dielectric analysis of nonaqueous colloidal systems. Analogous to soot-contaminated lubricants (Chapter 10), ERFs can be described as 

The electrostatic polarization theory is commonly employed to describe ER response. The model assumes that ER fluids are dispersions of nonionic polarizable particles in a low dielectric medium and that free charges and charge-transfer electrochemical processes can be neglected. This model is based on the fact that, due to the permittivity mismatch between the particles 6p and the continuous phase e, the dipolar particles are polarized and aligned with the neighboring particles. When an electric field is superimposed on the point dipole interaction, the orientation of the dipoles in relation to the exter- 

no double layer interfacial polarization or charge-transfer effects are observed even at the mHz frequencies. 

FIGURE 12-8 Impedance diagram representing dielectric behavior of elec-trorheological fluids 

FIGURE 12-9 Impedance data representing dielectric behavior of elec-trorheological fluid A. Bode impedance plot B. complex modulus plot C. Nyquist complex impedance plot 

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